Why rainwater cannot sustain a steamship's boilers

Could steam warships harvest rainwater as boiler feedwater?

Only as a supplement; collection cannot supply the enormous volume the boilers require.

The proposal addresses feedwater quality but not the scale of steam consumption. Rain can be collected and was considered as a supplementary source. A warship's boilers, however, require far more water than its exposed surfaces can gather reliably. Quantity rather than purity is the decisive constraint, keeping condensers and stored fresh water central to steam-plant logistics.